The Cycles of the Moon. Moon Basics…? What is the period of the Moon? What are the phases of the Moon? When can you see the different phases of the Moon?

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Presentation on theme: "The Cycles of the Moon. Moon Basics…? What is the period of the Moon? What are the phases of the Moon? When can you see the different phases of the Moon?"— Presentation transcript:

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The Cycles of the Moon

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Moon Basics…? What is the period of the Moon? What are the phases of the Moon? When can you see the different phases of the Moon? Does the Moon rotate as is revolves? Does the Moon cause our tides? What are tides? What are eclipses? Can we predict them?

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Sidereal Period (1) The Sidereal period is the time it takes the moon to go around Earth WITH RESPECT TO THE STARS. Start with the moon lined up with some background stars. Now have the moon revolve around Earth.

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Sidereal Period (2) Sidereal Period days From our position on Earth, the moon goes around and then is again lined up with the stars behind it.

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Sidereal Period (3) Sidereal Period days Note, however, that the moon no longer lines up with the Sun. It would need to go a bit further for that.

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Synodic Period Sidereal days Synodic days The Synodic period is the time it takes the moon to go around Earth WITH RESPECT TO THE SUN. The moon must go a bit further to line up with the Sun again.

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1 st Quarter Full Moon 3 rd Quarter New Moon Waxing Crescent Waxing Gibbous Waning Gibbous Waning Crescent NoonMidnight 3 pm 6 pm 9 pm 9 am 6 am 3 am W E Which way would you look to see…? RiseSet If you went out at 6 pm on the night of the full moon, which way would you look to see it? East West You would look to the East. The Full Moon would be rising on your eastern horizon. Using the paper method 6 pm is on the East side.

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1 st Quarter Full Moon 3 rd Quarter New Moon Waxing Crescent Waxing Gibbous Waning Gibbous Waning Crescent NoonMidnight 3 pm 6 pm 9 pm 9 am 6 am 3 am Which way would you look to see…? If you went out at 6 pm on the night of the waxing crescent, which way would you look to see it? Rise Set East West Using the paper method 6 pm is on the West side. You would look to the West. The waxing crescent would be setting in the west.

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1 st Quarter Full Moon 3 rd Quarter New Moon Waxing Crescent Waxing Gibbous Waning Gibbous Waning Crescent NoonMidnight 3 pm 6 pm 9 pm 9 am 6 am 3 am Clockwise = West Counterclockwise = East Which way would you look to see…? If you went out at 6 pm on the night of the full moon, which way would you look to see it? In your head method Start at the time Rotate toward the phase You would look in a counterclockwise direction… East. The Full Moon would be rising on your eastern horizon.

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1 st Quarter Full Moon 3 rd Quarter New Moon Waxing Crescent Waxing Gibbous Waning Gibbous Waning Crescent NoonMidnight 3 pm 6 pm 9 pm 9 am 6 am 3 am Clockwise = West Counterclockwise = East Which way would you look to see…? If you went out at 6 am on the night of the waning gibbous, which way would you look to see it? Start at the time Rotate toward the phase You would look in a clockwise direction… West.

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Other websites A good tool to test yourself on moon phases can be found at: This tool requires JAVA. This website also has a good moon tutorial. This is a great animation of moon phases!

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The Tides Tides are due to gravitational force on Earth from Moon – force on near side of Earth is greater than force on far side. Water can flow freely in response.

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Spring and Neap Tides The Sun is also producing tidal effects, about half as strong as the Moon. Near Full and New Moon, those two effects add up to cause spring tides. Near first and third quarter, the two effects work at a right angle, causing neap tides. Spring tides Neap tides

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The Tides Tides tend to exert a “drag” force on the Earth, slowing its rotation. This will continue until the Earth rotates synchronously with the Moon, so that the same side of the Earth always points toward the Moon.

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Acceleration of the Moon’s Orbital Motion Earth’s tidal bulges are slightly tilted in the direction of Earth’s rotation. Gravitational force pulls the moon slightly forward along its orbit. This causes the Moon to recede at 2” per year. (3.8 cm)

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The Tidally-Locked Orbit of the Moon The Earth also exerts tidal forces on the moon’s rocky interior.  It is rotating with the same period around its axis as it is orbiting Earth (tidally locked).  We always see the same side of the moon facing Earth.

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Eclipses Eclipses occur when Earth, Moon, and Sun form a straight line

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Motion of the Moon Eclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane.

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Conditions for Eclipses (1) A solar eclipse can only occur if the moon passes a node near new moon. The moon’s orbit is inclined against the ecliptic by ~ 5 0. A lunar eclipse can only occur if the moon passes a node near full moon.

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Lunar Eclipses Earth’s shadow consists of a zone of partial shadow, the Penumbra, and a zone of full shadow, the Umbra. If the moon passes through Earth’s full shadow (Umbra), we see a lunar eclipse. If the entire surface of the moon enters the Umbra, the lunar eclipse is total.

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A Total Lunar Eclipse

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Aug 2007 Eclipse

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A Total Lunar Eclipse A total lunar eclipse can last up to 1 hour and 40 min. During a total eclipse, the moon has a faint, red glow, reflecting sun light scattered in Earth’s atmosphere.

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Lunar Eclipses: Typically, 1 or 2 lunar eclipses per year.

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Solar Eclipses The sun appears approx. as large in the sky (same angular diameter ~ ) as the moon.  When the moon passes in front of the sun, the moon can cover the sun completely, causing a total solar eclipse.

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Annular Solar Eclipses The angular sizes of the moon and the sun vary, depending on their distance from Earth. When Earth is near perihelion, and the moon is near apogee, we see an annular solar eclipse. PerigeeApogeePerihelionAphelion